Shortly after the publication in 1956 of what is now described as the most important book of socialist revisionism of the last century, its celebrated author Tony Crosland found himself being questioned about it over dinner by an attractive young American woman he had recently met. "What exactly is 'The Future of Socialism'?" she asked. "Is it one of those pamphlets?" Her question pleased him greatly and he gave her a marked copy, annotated with the chapters she should skim and those she should skip altogether, in order to provide her with an appropriate grounding in political philo- sophy, sociology and economics.

Theirs was to be a meeting of minds, as well as a passionate love affair which lasted until his untimely death. It was an extraordinary relationship because she could meet him at every level. Susan Crosland, who has died aged 84, was brave, clever, funny, beautiful and smart. She also had a steely strength which, after their marriage in 1964, she used with considerable effect to promote her husband's frontbench career within the Labour party and thus provided a charming foil which served to counter his own somewhat Olympian manner, often perceived as arrogance.

She was born Susan Barnes Watson in Baltimore, Maryland, and brought up in an environment she herself described as not having fully recovered from the trauma of the civil war and the "reconstruction" of the south. She was the younger daughter of Mark Skinner Watson, a Pulitzer prize-winning war correspondent on the Baltimore Sun who was also awarded the presidential medal of freedom. Her mother, Susan Owens, was an early convert to women's emancipation and as a young reporter on the Sun had flown in a small plane over Baltimore scattering leaflets encouraging women to vote.

The girls were strictly raised but when Susan went to Vassar college, New York, aged 17, she was by her own admission rather "wild", but not "fast". Living at home after graduation, she taught at the Baltimore Museum of Art before marrying Patrick Skene Catling, a reporter on the Baltimore Sun, in 1952. The marriage was already rocky in 1956 when Catling was posted to the Sun's London bureau and Susan accompanied him with their two small daughters and first engaged with the capital's political and intellectual society, of which Tony Crosland was then a famously rude, famously brilliant and famously charming star. The Catlings fell in love with London and although the Sun assignment ended after two years, they returned almost immediately to live in London permanently.

Catling initially worked on the Guardian – and later for Punch magazine – but in order to bolster the family finances, Susan Barnes, as she called herself professionally in order to avoid using the journalistically distinguished names of either of her parents or that of her husband, also sought work in newspapers. She apparently had little difficulty in persuading John Junor, the editor of the Sunday Express, who was notoriously susceptible to beautiful young women, that he should employ her. After her first commissioned article about travel was published, she was offered a contract, the value of which she managed to push up by 80% through artful negotiation.

But despite the help Catling had initially given in her new career – they divorced in 1960 shortly after it had started – Susan swiftly proved she was a natural journalist with an instinct for drawing people out during interviews and a sure touch in understanding the subtleties in her subjects' personalities. The Susan Barnes Interview was a regular and popular feature in the Sunday Express until she married Crosland and he insisted that she should not write for a Conservative-supporting newspaper while he was looking to join the cabinet. She moved to the Sun, before it was bought by Rupert Murdoch in 1969, and then in 1970 found her metier writing lengthy, in-depth profiles of significant public figures for Harold Evans's Sunday Times. Her articles in those years were must-reads.

A flavour of her style of interview – though not, on this occasion, rewarded with the success she usually achieved – is given by an account from Tony Benn's Diaries in 1965: "She ... asked a hundred trivial questions. Why do you keep your hair short? What do you think the Evening Standard meant by saying that you were a Scoutmaster? It was entirely inconsequential and I cannot think that anything helpful will come out of it."

The Croslands and the Benns were neighbours and friends, despite coming from different wings of the Labour party, and presumably for that reason Susan had agreed that Benn could vet the article. He found it "unspeakable". He wrote: "It was the bitchiest, most horrible thing I've ever read and I decided to be bold and rang her up and asked her not to publish it. She was much taken aback, no doubt hurt, but she assented immediately. I should never have accepted in the first place."

She managed to maintain her career while being a supportive cabinet wife. Like several others of her generation – Audrey Callaghan, Edna Healey, Caroline Benn among them – Susan Crosland was willing to put up with the limitations of being married to a great man while having her own strengths. She stuck out in a crowd. One friend, Therese Lawson, said of her: "Susan has an aura about her. It is difficult to be in the same room and not notice her."

Tony Crosland had a low boredom threshold and would sometimes duck social engagements; Susan often represented him. Barbara Castle commented that he sent her out to pick up the gossip, and Susan certainly enjoyed the political salons, but she also recognised how she could help ameliorate her husband's sometimes brash behaviour with her charm. "I found myself talking to Tony Crosland's wife, Susan Barnes, which was very nice indeed," writes Richard Crossman in 1966. And in 1969, at a production of Die Meistersinger at Covent Garden, when neither his wife nor Tony were present, Crossman notes: "She looked very beautiful with her skirts far above her knees and her dress right down on her breasts ... it was very nice just to have Susan and myself ... [the performance] was dramatic and dynamic. We went out enormously exhilarated ..."

When Tony Crosland, then foreign secretary, died aged 58 following a stroke in 1977, his widow helped alleviate her grief by writing his biography. It took her four years and it is an unusual book, written from inside the marital home, but it is also an important contribution to understanding the Labour party politics of those years which stands as a testament to her skills. She refused an invitation to stand as parliamentary candidate in Grimsby in succession to her husband, declined a life peerage and instead resumed her career in journalism. She also began writing novels: Ruling Passions (1989); Dangerous Games (1991); The Magnates (1994); and The Prime Minister's Wife (2001). She published two books of collected articles, Behind the Image (1974) and Looking Out, Looking In (1987), and, in 2002, Great Sexual Scandals. Her last novel, which was partly autobiographical, was edited by and dedicated to her great confidant Auberon Waugh, with whom she enjoyed 16 years of friendship until his death in 2001. She was working on a memoir of their relationship.

Her last years were clouded by ill-health, triggered by a riding accident as an 18-year-old which brought arthritis in middle age and the need for hip and shoulder replacement operations. After one of these, she contracted the superbug MRSA, as an NHS patient in a London hospital. She continued to use the NHS, although her politics were adopted from her late husband. According to a family friend: "She bought Tony's politics like someone buys a watch as a work of art because the mechanism is so beautifully constructed, and not because it tells the time particularly well."

By the time of her death, she was profoundly disabled. "I hope to continue to be stoical rather than bitter," she said. "I'm an optimistic person but I've sometimes been disappointed in my optimism." Until an hour before she died, she was singing with one of her daughters. She leaves two daughters, Sheila and Ellen-Craig, four grandchildren and one great-grandchild.

Diana Melly writes: Although Susan was often in a lot of pain, and latterly always so, she never complained. She cared about her appearance, and had her shoes dyed in bright fluorescent colours to match her walking sticks. Eventually, confined to a wheelchair, and wearing a flower tucked behind her ear to disguise her hearing aid, she still went to the opera, the theatre and saw her friends. She also managed that most difficult of arts, how to receive the care that she needed gracefully and gratefully, and with buckets of charm.

• Susan Barnes Crosland, journalist and author, born 23 January 1927; died 26 February 2011